Variation of the 3' telomeric overhang lengths in human cells

The telomeric G-rich 3' overhang is important for the maintenance of chromosomal integrity by stabilizing T-loop structure in which the 3' overhang invades the double-stranded telomeric DNA. However, the 3' overhang length has not been examined in different human cell lines, and its regulatory mechanism has not been revealed. In this study, we examined overhang length in 56 human cancerous cell lines and five normal cell lines, originated from various tissues. In cancer cells, relative overhang length existed in a wide range from 23% to 308% and showed no significant association with tissue types although short overhang was noted in brain, cervix, and colorectal cells. Normal cells exhibited overhangs in the range from 92% to 202%, which were relatively longer than those seen in cancer cells (p = 0.002). The overhang length was positively correlated with telomere length (p < 0.001), and showed no correlation with mRNA levels of hTERT, a catalytic protein of telomerase, POT1, an overhang binding protein and TPP1, a POT1 interacting protein. This study demonstrates a broad distribution of overhang length in human cells, suggesting a dynamic regulation of 3' overhang length. The overhang length seems to be closely associated with telomere length and might be regulated by multiple mechanisms.